At present, in sanitary goods such as a disposable diaper, a sanitary napkin, a so-called incontinence pad and the like, a water absorbing resin (particulate water absorbing agent) and a hydrophilic fiber such as pulp aiming at absorption of body fluids have been widely employed as their component material.
Conventionally, known water-absorption properties expected for the water absorbing resin as described above involve many characteristics (parameters) such as centrifuge retention capacity, absorbency against pressure, water-absorption speed, liquid permeability without pressure, liquid permeability under pressure, impact resistance, resistance to urine, flowability, gel strength, color, particle size and the like. In addition, with regard to the same physical property (e.g., centrifuge retention capacity), many definitions according to various aspects (parameter measurement methods) were proposed.
For example, Document 1 proposes a water absorbing resin that is excellent in liquid permeability and impact resistance. Documents 2 to 4 propose a water absorbing resin subjected to surface crosslinking in which an aqueous cation solution is used. Document 5 proposes a water absorbing resin and the like in which the moisture content was regulated for ameliorating fragility of the particles. Furthermore, Document 6 proposes a water absorbing resin having a certain moisture content and having a certain absorbency against pressure. Additionally, Document 7 proposes a hydrogel subjected to coating with a steric or electrostatic spacer.
The water absorbing resins (particulate water absorbing agents) which have been developed while focusing on these many physical properties have been produced and used through targeting these physical properties, or as products having such physical properties. However, even though the aforementioned numerous physical properties (e.g., “centrifuge retention capacity”, “absorbency against pressure” and the like) were regulated, powder conveying property was inferior. Furthermore, there still exists a problem of hardly achieving sufficient performance in practical applications in absorbent cores such as disposable diapers and the like.    [Document 1] U.S. Pat. No. 6,414,214    [Document 2] U.S. Pat. No. 6,620,889    [Document 3] JP-T-2002-539281    [Document 4] JP-T-2003-529647    [Document 5] JP-A-H9-124879    [Document 6] U.S. Pat. No. 6,323,252    [Document 7] JP-T-2004-517173    (“JP-T”: Japanese translation of PCT international application)